Phase diagrams of poly(siloxane)/liquid crystal blends

Abstract

Phase diagrams of blends of poly(methylphenylsiloxane) in short PMPS and two low molecular weight liquid crystals (4-cyano-4Ј-n-pentyl-biphenyl and an eutectic mixture of paraphenylenes) are reported. Two polymers with very different weight-average molar masses are considered in an evaluation of the loss of miscibility resulting from a known increase in the weight-average molar mass. The experimental diagrams have been constructed via polarized optical microscopy and are rationalized in terms of the Flory-Huggins theory of isotropic mixtures and the Maier-Saupe theory of nematic order. The results show a good agreement between the theory and experiments and reveal a remarkable enhancement of miscibility with respect to similar systems involving poly(dimethylsiloxane). Variations of the interaction parameter with the temperature are compared for different systems of polysiloxanes. The effects of the nature of the liquid crystal and the polymer molar mass on the parameter are evaluated.

Preferential solvation of the eutectic mixture of liquid crystals E7 in a polysiloxane

“…An increase of nearly 20 8C was found in the presence of 80 wt% PMPS which was attributed to the preferential solvation of E7 but no evidence of this phenomenon was given so far for poly(siloxane) systems. However, corresponding phase diagrams of PMPS/5CB systems do not show such a behaviour, although the PMPS was characterized by the same molecular weight [13]. Indeed, the NI transition temperature was found to remain constant at 35 8C throughout the whole phase diagram.…”

“…In the majority of cases reported in the literature by us [7,8] and other groups [9,10], these transition temperatures are hardly modified in the presence of a polymer. There are, however, some exceptions which remain to be elucidated involving a phase separation of the constituents of the multicomponent mixture E7 in the presence of certain polymers [1,[11][12][13]. A possible interpretation of this phase separation is given by the preferential solvation of the constituents of E7 towards the polymer under certain conditions.…”

“…Gogibus et al [13,17,18] reported an investigation of the morphology and phase behavior of various linear poly (siloxane) and low molecular weight LC systems. In particular, they considered systems involving the polymers poly(dimethylsiloxane) (PDMS) [17,18] and PMPS [13], and the LCs 5CB and E7.…”

“…In particular, they considered systems involving the polymers poly(dimethylsiloxane) (PDMS) [17,18] and PMPS [13], and the LCs 5CB and E7. Trends similar to those of the PBA/E7 system were also observed on the PMPS/E7 system as presented in Fig.…”

Nematic–isotropic transition in polymer‐confined and polymer‐free liquid crystal mixtures

“…Also the heterogeneity of LC droplets formed after photo polymerization of isotropic E44/NOA65 mixtures is attributed to a fractionation caused by different affinities of the LC compounds to the NOA65 networks 9. In other investigations of the morphology and the phase behavior of various LC/polymer systems,10–14 the n–i transition temperature, that is, the clearing temperature T c , was identified as a highly sensitive indicator for changes of the composition and was used for the comparison of different samples.…”